Liquid chromatography measurement systems such as high performance liquid chromatography (HPLC) and ultra HPLC (UPLC®) systems typically employ injection valves having a rotary shear seal. A force of several hundreds of pounds or more is applied between the rotor and stator to seal against pressures that can exceed 15,000 psi. The force is maintained while the rotor rotates between valve switch positions, thereby placing stringent requirements on the quality of the sealing surfaces. The injection valves are typically intended to operate for tens of thousands of cycles without excessive wear and leakage.
HPLC and UPLC instrument manufacturers anticipate that future instruments will require sealing pressures of injection valves to exceed 20,000 psi. Intrinsic limitations in the material properties of the stator and, in particular, the polymeric rotor are not likely to be overcome with incremental improvements in materials and design.
U.S. Pat. No. 6,193,213 discloses a method for varying the force or pressure applied between the stator and the rotor during rotation of the rotor in a conventional rotary shear injection valve. In particular, a lower force is applied when the required sealing pressure is low or when the injection valve is rotated between two switch positions to reduce wear. A greater force is generated at other times to maintain a proper seal and when the valve is not in transition between switch positions. The force applied between the stator and the rotor is controlled by the pressure of a fluid supplied to the injection valve. This technique requires high-pressure fluid control and sealing to operate. One significant disadvantage is the potential for leakage of the hydraulic fluid used to vary the applied force.
The present invention addresses the need for a high pressure rotary seal valve that overcomes the problems identified above and can seal to pressures greater than 20,000 psi for tens of thousands of cycles.